Cook ground beef and onion in a Dutch oven over medium-high heat, stirring until beef crumbles and is no longer pink; drain. Add beans, corn, tomato sauce and seasoning mix; stir until blended. Simmer over medium heat 10 minutes.
Pour half of beef mixture into a lightly greased 13"x9" baking pan. Top with 1 1/2 cups each of cheese and crushed chips; top with remaining beef mixture and remaining 1 1/2 cups each of cheese and chips. Bake, uncovered, at 350 degrees for 25 to 30 minutes or until bubbly and golden. Sprinkle with chopped tomatoes and green onions, if desired.